Human immunodeficiency virus-1 (HIV-1) has been identified as the etiological agent responsible for acquired immune deficiency syndrome (AIDS), a fatal condition that arises by the invasion of the virus on various cells of the human immune system, mainly the T-cells. HIV is a member of the lentivirus, a subfamily of retrovirus, which have a single stranded ribonucleic acid (RNA) as the genetic material. The virus has the ability to integrate its genetic information into the genome of the host cell thereby blocking normal genetic flow of information in the cell. The virus then takes over the cellular machinery and replicates itself by synthesizing its own proteins and packaging the genetic material. Another feature of HIV infection is that the virus does not keep replicating itself all the time. There are “window periods” after infection, during which replication is not observed. This is regarded as a silent phase where the effect of the infection during which immune deficiency is not detected. A critical aspect of HIV infection is that, it infects and invades cells of the immune system, resulting in break-down of the body's immune system and rendering the patient susceptible to opportunistic infections and conditions like neoplasms which arise due to immune system inactivation. HIV-1 is cytopathic for T4 lymphocytes, cells of the immune system that express the cell surface differentiation antigen CD4. In addition to CD4+ T cells, the host range of HIV includes cells of the mononuclear phagocytic lineage, including blood monocytes, tissue macrophages, Langerhans cells of the skin, and dendritic reticulum cells within lymph nodes.
Worldwide, researchers have been engaged in studies to develop effective therapeutic antiviral agents and vaccines against this deadly virus. Currently accepted strategies are mainly based on non-nucleotide analog inhibitors of reverse transcriptase, such as Nevirapine (BI-RG-587), TIBO (R82913), pyrinodes (such as R-697,661 and L-696,227), bis(heteroary) piperazines (BHAPs, such as U-87201E and U-90,152), atevirdine mesylate (ATV) and R-89431; HIV protease inhibitors, include substrate analogs and non-analogs, such as Ro 31-8959, A-77003 and A-80987; HIV Tat protein inhibitors, such as Ro 5-3335 and Ro 27-7429; blockers of viral entry into cells, such as soluble CD4 protein (sCD4), and chimeric sCD4 derivatives, such as CD4-lgG and CD4-PE40; blockers of HIV RNaseH activity, such as the AZT derivative azidothymidine monophosphate; drugs that alter the intracellular milieu to create conditions less favorable for viral replication, such as the free-radical scavengers and glutathione-level restoring drugs (N-acetylcysteine and similar drugs), and thalidomine (which seems to lower blood TNF-.alpha. levels). Efforts have also focused on manipulation of the immune system and viral replication with naturally-occurring cytokines and lymphokines, or other agonists or antagonists of these systems. One of the drugs most frequently used is azidothimidine (AZT). Antiviral therapies with pharmaceuticals that inhibit the replication of HIV have been found to decrease plasma virus to undetectable levels. Combination antiviral HIV therapy with Protease Inhibitors (PI) and Reverse Transcriptase (RT) inhibitors has provided Highly Active Antiviral Therapy (HAART). HAART results in the rapid cessation of viral replication and the decline of plasma virus to undetectable levels within 4-8 weeks. More recently, short interfering RNA (siRNA) has been tried against HIV infection. The property of siRNA that is made use here is that the binding of these small RNAs to mRNA would result in the cleavage of the mRNA which consequently inhibits protein synthesis.
Even before siRNA-based therapy has reached the clinical trial stage for use as an anti-HIV mechanism, probability of failure exist owing to the fact that exact complementarity is a necessity for siRNA activity. HIV is observed to constantly mutate its genome and this would result in rendering the siRNA-mediated inhibition a failure. However, miRNAs may offer a more effective alternative since they require incomplete complementarity.
Recently it was shown that human miRNAs can down regulate Hepatitis C Virus (HCV) and Primate Foamy Virus-1 (PFV-1) mRNA. The inventors have observed that human microRNAs hsa-mir-29a, hsa-mir-29b and hsa-mir-29c, which were predicted by all the programs, exclusively target the nef gene of HIV-1. Viral genes like tat and the gene coding for reverse transcriptase, as well as genes of host origin required for viral transcription have previously been targeted using siRNAs. In the present study, the inventors have shown that human microRNAs may target HIV-1 genes. These miRNAs have highly conserved targets in HIV-1 and related lade sequences. They are expressed in T-cells, the natural site of infection by HIV-1 infection and their expression level may vary between individuals. In summary, our study implies that human miRNAs have the potential to affect expression of HIV-1 genes and may in future be used to develop therapeutic approaches to inhibit HIV-1.
Drawbacks of Existing Therapies
Although AZT has proved effective in many cases, lowering mortality rates, the virus develops resistance to AZT, and the drug has significant and adverse side effects.
In most instances, HAART alone does not lead to complete immune recovery. Another drawback of HAART is that HIV develops resistance to it. Moreover, it now appears that many individuals may not be able to take HAART indefinitely, due to serious long-term side effects. As many as 40%-60% of patients who have received HAART for greater than one year have developed symptoms of Cushing's Syndrome, with hyperglycemia, hyperlipidemia, centipetal fat distribution, and peripheral muscle wasting.
Even before siRNA-based therapy has reached the clinical trial stage for use as an anti-HIV mechanism, probability of failure exist owing to the fact that exact complementarity is a necessity for siRNA activity. HIV is observed to constantly mutate its genome and this would result in rendering the siRNA-mediated protein inhibition a failure.
Accordingly, there is a need for new safe and efficient therapeutic and preventive methods for HIV-infections. The invention addresses this need in the field.